I. Field of the Invention
The present invention relates generally to power inverters of the type used in hybrid electric vehicles, electric vehicles, and fuel cell vehicles, and more particularly, to such a power inverter with noise compensation.
II. Description of Related Art
In view of the high cost of hydrocarbon fuel, hybrid electric vehicles, electric vehicles, and fuel cell vehicles have enjoyed increased popularity. In such vehicles, one or more electric motors are utilized to assist the engine to provide more traction power as well as to regenerate power to charge the battery. For both driving the vehicle as well as regenerating the battery, a power inverter is required to complete the power conversion between alternating current used to power the motor and generated by the motor during a braking cycle, and direct current. The direct current is used to store power in the battery during a regeneration period of operation of the vehicle while DC power from the battery is used to power the motor for increased traction and/or acceleration.
For a fall hybrid system, the electric motor typically has a power capacity of at least 50 horsepower in order to power the vehicle independently without the gasoline engine. This high power rating for the electric motor results in high voltages and high current requirements for the hybrid electric vehicle.
In order to obtain proper operation of the hybrid electric vehicle, current sensing is an important function for the electrical drive system of the vehicle. The typical HEV system utilizes electric motors to assist the traction torque when acceleration is required as well as to regenerate power during braking. Previously, the hybrid controller regulates the driving current of the electric motor and thus controls the output torque for the electric motor system. Consequently, current sensing results are very important to accurately control the performance of the hybrid vehicle. Such performance factors include power transition, smoothness, acceleration quality, braking performance and the like. Conversely, rough or inaccurate current sensing quality may affect the driving quality, the overall performance of the electric vehicle and, in extreme cases, even cause system failure.
Accurate current sensing for the power inverter in an REV, however, is oftentimes difficult to obtain due to the number of electromagnetic noise (EMI) sources within the power inverter. For example, a typical power inverter utilizes high battery voltage which is electrically connected to the HEV motor through insulated gate bipolar transistors which operate under the control of a gate driver. The gate driver selectively switches the transistors in the gate assembly to produce three phase alternating current electrical output for the HEV motor. The switching of the high current and high voltage within the power inverter also creates excessive noise.
Typically, the power inverter for an HEV uses pulse width modulation (PWM to regulate the phase currents and thus the torque of the REV motor. The switching frequency for the gate assembly transistors is typically in the range of 1 kilohertz to 20 kilohertz and this noise typically enters the AC output to the motor.
Although the switching of the gate transformers in the gate assembly for the inverter constitutes a major source of EMI in the inverter, there are other sources of EMI in the inverter which also enter the current output to the motor. For example, many HEV power inverters include different DC voltages so that DC-DC converters, oftentimes using PWM switching power supplies, also add to the EMI within the inverter These other sources of EMI, furthermore, oftentimes operate at different frequencies than the gate assembly for the power inverter.
Since EMI is present on the current sensor output, the current sensor for the previously known power inverters provides an inaccurate signal to the controller for the power inverter. Since the controller controls the activation of the gate assembly, and thus the current to the HEV motor, less than optimal operation of the electric motor results.